In addition to the intrarenal mechanisms which control renin release, high pressure and low pressure intravascular mechanoreceptors exert a baroreflex influence on renin secretion by the kidney. Numerous studies in the dog have shown that this neural control of renin secretion plays an important role in the regulation of blood pressure, blood volume, and blood flow to specific organs. Furthermore, changes in receptor sensitivity or set-point, or in the central processing of receptor information may play a role in the renal response to congestive heart failure and hypertension. Recent data from canine studies have also demonstrated that extremely small changes in renal sympathetic nerve discharge are capable of directly stimulating renin release and can also facilitate the nonneural release of renin by the kidney. These studies are significant because they may explain how the kidney becomes reset to higher operating pressures during hypertension. However, there data from man and nonhumna primate studies which suggest the afferent neural control of renin secretion is different than in the dog. The cardiopulmonary volume receptors appear to be much less important in primates which may rely more on changes in arterial pressure to control renin secretion. Unfortunately, because of their invasive nature, definitive studies can not be performed in man. For this reason the nonhuman primate must be used to study the baroreflex control of renin secretion. The studies in this proposal will use the primate Macaca fascicularis as a model for the neural control of renin release in man to answer the following specific questions: 1) What is the relative importance of cardiopulmonary low pressure receptors and arterial high pressure receptors in the control of renin secretion in the primate? 2) What is the relationship between renal sympathetic nerve activity and renin secretion by the primate kidney? 3) How do the extrarenal high and low pressure receptors interact with the intrarenal vascular mechanism to stimulate renin secretion? To answer these questions an isolated-perfused carotid sinus preparation will be used to derive complete baroreflex renin response relationships in the primate. By selectively stimulating high and low pressure baroreceptor afferents, it will be possible to determine the modulatory role of each set of receptors on renin release. The results of these experiments will be highly relevant to further understanding of cardiovascular control mechanisms in man.